Pipettes are commonly utilized to aspirate a fluid from one container or other source and to dispense the fluid to a second container or other receptacle. Since the fluid being aspirated and dispensed is frequently analyzed or otherwise tested after being dispensed, and in order for such testing or analysis to be accurate, it is important that a sample not be contaminated by fluid from a prior aspirated sample. While it is possible to wash a pipette tip between aspirations in order to reduce or eliminate such contamination, and for some pipette systems, particularly those utilizing fluid displacement, this is frequently done, washing the tips is expensive and time-consuming, and it is frequently difficult to remove all contaminants. Therefore, for many pipettes, particularly air displacement pipettes, it is cheaper and easier to replace the pipette tip after each use.
However, when a pipette tip is mounted to the nozzle, it is important that the tip be mounted with sufficient force to seal the nozzle so that fluid being aspirated and dispensed does not leak around the tip-nozzle junction, thereby preventing accurate quantities of fluid from being aspirated and dispensed, and the tip must be mounted with sufficient force to prevent the tip from falling off. However, if the tip is mounted with too much force, it can become difficult to remove the tip from the nozzle after use, resulting in significant strain on the operators hand. For this and other reasons, an operator working in a laboratory or other facility where large numbers of tips are replaced each day may experience repetitive stress injuries with current pipette designs as a result of repeated tip removals.
Heretofore, control on the force applied in mounting a tip to a nozzle has generally relied on the skill of the person doing the mounting. Thus, while for an illustrative embodiment, only two pounds of force may be required to properly mount a tip to the nozzle, operators may inadvertently be applying 10 to 15 pounds of force in mounting the nozzle, making nozzle removal far more difficult than necessary. However, without tactile guidance, an operator might overcompensate for this problem and not properly mount a nozzle. Further, while some tip removal mechanisms have existed for pipettes in the past, these have generally been manually operated and, since they have generally not controlled tip mounting force, they have frequently required that substantial force be applied by, for example, the operator's thumb to successfully effect tip removal. This operation is therefore another potential cause of repetitive stress injuries. Alternatively, such tip removal schemes have been motor driven, increasing the size, cost and complexity of the pipette.
A related problem is that there are a variety of tips available for use with a given pipette and the pipette volume settings, particularly where these settings are automatically performed, need to be slightly adjusted for some tips to obtain the desired volumes of aspirated and/or dispensed fluid. The tips may for example have different length, volume, orifice diameter/size, shape and/or surface treatment (for example a low liquid retention coating). The tips may also be filtered or unfiltered, and if filtered, may have various special filtering elements, the presence and nature of filtering elements being a major factor in requiring volume adjustments for the pipette. While provision may be made for the user to input information on the tip being used either on the pipette or on a processor used therewith, this can be burdensome for the operator where a large number of pipetting operations are being performed. It also provides a source of pipetting error where the operator either forgets to identify a special tip used for a given operation or makes an erroneous entry, either because the operator doesn't know the tip used or enters tip information incorrectly. It is also possible that the operator may select the wrong tip for a particular pipetting operation. It would therefore be preferable if the pipette could easily and quickly identify the tip being mounted as part of the tip mounting process without requiring any operator input, and could provide some type of feedback to the operator, for example when there is a change in tip used, to minimize inadvertent use of the wrong tip.
A need therefore exists for improved pipettes which overcome the various tip mounting, tip removal and tip identification problems identified above.